[R] problem with abline for x.y
Deepayan Sarkar
deepayan at stat.wisc.edu
Fri Feb 20 16:11:53 CET 2004
On Friday 20 February 2004 08:17, Michael Friendly wrote:
> I'm trying to do a sunflowerplot of Galton's data, with both regression
> lines and data ellipses,
> and I must be doing something wrong, because the lines do not intersect
> at \bar{x}, \bar{y}.
> The problem is likely in the line for x.y, but I don't know how to
> specify that correctly.
[...]
> # both attempts plot the same, wrong regression lines
> y.x <- lm(parent ~ child, weights=frequency)
> abline(y.x)
> x.y <- lm(child ~ parent, weights=frequency)
> abline(x.y, col="gray")
>
> attach(galton2)
> y.x <- lm(parent ~ child)
> abline(y.x, lwd=2)
> x.y <- lm(child ~ parent)
> abline(x.y, col="gray", lwd=2)
This looks like you are getting a line with equation of the form
x = c0 + c1 y
and then plotting the line
y = c0 + c1 y
You should probably do
cx.y <- coef(x.y)
cx.y <- c(-cx.y[1], 1) / cx.y[2]
abline(cx.y)
[Code untested, though]
Deepayan
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